1. Field of the Invention
The present invention relates to a stencil printing machine and, in particular, to a stencil printing machine having a function of maintaining confidentiality of a used master (stencil sheet).
2. Description of the Background
In a stencil printing machine, a master wound like a roll is pulled out and a content of an original manuscript is transferred onto the master by thermal perforation (plate making) with using a thermal head. The master subjected to the plate making is wound around a plate drum (stencil plate mounting body) and an ink is supplied to a perforated portion in the master. A printing paper sheet is then pressed against the master so that the content of the master is transferred onto the printing paper sheet. The master after the printing process, that is used master, is stripped from the plate drum by a plate ejecting device immediately before performing of the next plate making process. The used master is stored in an ejected plate box or the like in the printing machine. When a predetermined amount of the used masters have been stored, the masters are taken out of the ejected plate box or the like to the outside of the printing machine and discarded in a trash box or the like.
However, since the master used in the stencil printing machine has the content of the original manuscript transferred thereon by the perforation, it is possible to read the content even though the master is the used one. Therefore, though the content of the master requires confidentiality, there is a possibility that the secret is disadvantageously leaked to a third party or the like who has obtained the used master. Consequently, various stencil printing machines having functions of maintaining confidentiality which prevents reading the content of the master have been conventionally proposed.
As a conventional functions of maintaining confidentiality, there have been known the following techniques. In a technique (Patent Documents 1 to 3), a master is shrunk or melted by heating so that the master gets into an unreusable state. In a technique (Patent Documents 4 and 5), the mask is physically damaged by a sharp protrusion so that the master gets into an unreusable state. In a technique (Patent Document 6), a perforated portion is filled by applying a resin onto the surface of the master so that the master gets into an unreusable state.
In addition, there has been known the following technique. In a technique (Patent Document 7), a door of a printing machine housing an ejected plate box is bolted so that the used master is not freely taken out.
In the case of the techniques (Patent Documents 1 to 6) with performing processes such as heating, damaging, and the like for the used master, it is necessary to newly provide a device for performing the processes, and this naturally leads to increases in size, a number of parts and cost of an overall printing machine.
On the other hand, in the case of the technique (Patent Document 7) in which the door of the printing machine is bolted, since only the addition of a lock is required, it is possible to restrain increases in size, the number of parts, and cost.
However, in a stencil printing machine, since a plate drum and an ejected plate box are normally disposed adjacent to each other. Thus, when a jam occurs in the portion of the plate drum, it is necessary to take out the ejected plate box from the printing machine to fix the jam. Further, When the door of the printing machine is bolted, it is necessary to unbolt the door every time the jam occurs. Therefore, there have been problems that fixing the jam becomes very complicated and the functions of maintaining confidentiality can not be exercised during fixing the jam.    Patent Document 1: Japanese Patent Number No. 2828479    Patent Document 2: Japanese Laid-Open Patent Publication. No. 9-142001    Patent Document 3: Japanese Laid-Open Patent Publication No. 2002-86882    Patent Document 4: Japanese Laid-Open Patent Publication No. 6-40138    Patent Document 5: Japanese Laid-Open Patent Publication No. 2005-153474    Patent Document 6: Japanese Laid-Open Patent Publication No. 2003-136825    Patent Document 7: Japanese Laid-Open Utility Model Publication No. 61-31763
An object of the present invention is to provide a stencil printing machine in which, when a jam or the like occurs, a plate ejecting device can be easily taken out of the printing machine in a state where confidentiality is reliably maintained.